Lubricant composition



Staes LUBRICANT COMPOSITION Andrew D. Abbott, Ross, Califi, assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Filed Mar. 31, 1958, Ser. No. 124,872

5 Claims. (Cl. 252-321) peratui'e are keptas small. as possible. Lubricating oils containing 'such polymericfadditives are somewhat thickened at the higher temperatures normally encountered in engine operation While at the sametime retaining desirable low viscosity fluidity at cold starting temperatures. The ability of a lubricating oil to accommodate increased temperatures with a minimum decreaes in viscosity is indicated by its high Viscosity Index as derived from commonly accepted viscosity standards. Because of the aforementioned properties, these polymeric additives have been conveniently termed both thickeners and viscosity index improversf Polymers of alkyl'methacrylates are particularly efiective additives of the above type. Included are polyalkyl methacrylates in which the alkyl groups are mixtures of lower alkyl groups of'7 carbon atoms or less andhigher alkyl groups of 8 carbon atoms or more. Some of the moreimportant polymeric methacrylates also provide enhanced detergentproperties to mineral lubricating Oil compositions as well as desirable viscosity-temperature characteristics.

Among thefmore important polymeric viscosity index improvers and detergents of this type are t the copolymers of the aforementioned alkyl niethacrylates with monomers containing polar groups such as the MN.- Idialkylaminoalkylmethacrylates, the polyglycolrnonomethacrylates and the vinyl nitrogen heterocycles.

Mineral lubricating oils containing polymeric additives deposit-forming.materials such assludge andresins from oxidation in dispersion in the 'oil.' Among the moreiim portan-t additives of. this type {are theIessentially neutral ice containing the polymeric thickeners mentioned above has a decidedly adverse effect on the viscosity-temperature characteristics of the mineral lubricating oil compositions. There'is an undesirable'increase in the viscosity compared to the viscosity 'of the thickened mineral lubricating oil alone and the variations in viscosity with temperature changes of the oil are unfavorably exaggerated as indicated by the lowered viscosity index of the composition.

The above-mentioned adverse efiect on the viscositytemperature characteristics of the mineral lubricating oil compositions is of the greatest importance in the'case of the so-called multigrade lubricating oils developed for more effective lubrication over the wide temperature ranges commonly encountered in internal combustion engines. Polymeric thickenersjof the important polymethacrylate ester type are added to these oils to raise the viscosity index radially and thus enable a singleoil to meet the specification viscosity ranges of the two or three different SAE viscosity grades. The increase in viscosity, particularly at low temperatures where only certain viscosities can be tolerated; and the depreciation of the aforementioned critical viscosity index improvement of the thickened lubricating oil by the addition of the more important metal salt organic detergent additives referred to above may prevent an oil from qualifying as a multigrade oil. I l v The addition of the metal salt organic detergent additives; tothe thickened mineral lubricating oils has both an immediate adverse effect as desc'rib'ed above, and'al so a po'stponed efiect in that further undesirable increases in viscosity'and depreciation of the viscosity index are Ob} served over certain periods of time. This effect which has been'conveniently termed viscosity driftf is extre'rnely critical since an otherwise satisfactory "oil" may become completely unsatisfactory during th e' usual storage periods for lubricating oils. V I it-has now'been found that stable viscosity-temperature characteristics are providedirilmineral lubricating oil compositions comprising amajor portjonof' a a1 lubricating oil, a minor portion sufiic'irit to; improve the eating oil of -a metal salt organicdetergenf iadditrve I i selected from the classfcon'sisting"ot metalphena M zinc aromatic dithiophosphate and a minor portio cient tostabilize the viscosityof the mrneralflubrlcat 7 oil composition of 'dialkyl acylamide containin from 1 to 3 carbon atoms in the acyl'group and from t 3 carbon atoms in each allgylgroup'.

he mineral lubricating oil co tion possess unusually stable"viscosity ternperature charalkaline earth'metal petroleum sulfonates and thealkalin e earth metal phenates or their sulfurizedderivative'sIiAnother important type or metal salt organic detergent additive, namely the zinedithiophosphates imparts not only detergent characteristics but also oxidation'and corrosion inhibiting propertiesfto mineral "lubricating oil compositions. Y

have been combined to give mineral lubricating oil compositions having excellent 'detergeri-t properties alongwith.

superior viscosity-temp erature. characteristics. Unfortunately, it happens that theaddition of therirriportant v the viscosity index of the prse nt"corriiiosifio V v The two different classes ofadditives described above 5';

metal salt organic detergents to mineral .lubricatingcoils acteristics compared to minerallubricatingoil,

tions containing polymethacrylate "ester: viscosity imp'rove'rs in combination with rnetalfsalt f'org terg'ent additives 'withoutthe dialkyl acylamid ticularly in the case of the multigrade ilubrifza rig oils V where certain minimum low temperature viscos minimum 7 variations; in viscosit'y of; the. "0' ov temperaturera'nges are criticalft he outstanding pro ertrels" of the compositions according toitheinvnt appreciatedQ It isfifoundfthat the "viscosity practically unchanged, even over" ext ded .tirne. 35* FY T hedialkyl acylamides which are'used in 'ing oil compositions of the mens s-a by alkyl groups of from 1. to 3 carbon "to an acyl group of lto 3 'carb'on'a to m acylamides :in this" class ofi compounds 'fortnamide; dirnethyl actamidegi methyl-.thy p op Pa tented Mar. 28, 19st nipositibns dru s mge 1 amide and dipropyl propionamide. For present purposes dimethyl acetamide is preferred since it provides the most viscosity stable compositions at lowest concentration.

The metal salt organic detergent additives of the more important types such as are employed in the mineral lubricating oil compositions according to the present invention include the neutral alkaline earth metal petroleum sulfonates, alkaline earth metal phenates, sulfurized alkaline earth metal phenates and zinc aromatic dithiophosphates as mentioned above. These particular metallo organic additives are generally recognized as efiective lubricating oil detergents and inhibitors and should re quire no particular description here. Illustrative alkaline earth metal petroleum sulfonates include barium petroleum sulfonate, calcium petroleum sulfonate, magnesium petroleum sulfonate and slightly basic calcium petroleum sulfonates having a base ratio not greater than 0.6 (base ratio" being the ratio of basic calcium to total calcium). Only the substantially neutral sulfonates seem to have an adverse effect on the thickened mineral lubricating oils. Suitable alkaline earth metal alkyl phenates include calcium cetylphenate, calcium tetradecylphenate, barium cetylphenate, and sulfurized calcium cetylphenate. The aforementioned phenates preferably contain from to carbon atoms in the alkyl group and may be normal or basic in nature since both types alter the viscositytemperature characteristics of the thickened oils undesirably. The zinc aromatic dithiophosphates of the compositions of the invention are characterized by the presence of at least one aryl group. Illustrative thiophosphates of this type include zinc dodecyl phenyl thiophosphate, zinc dihexylphenyl dithiophosphate, zinc hexyl naphthyl dithiophosphate and zinc diamylphenyl dithiophosphate. Thiophosphates without aryl groups do not appear to affect the critical viscosity properties of the thickened compositions.

The polymeric methacrylate ester lubricating oil thickeners of the compositions according to the invention are also a recognized class of effective lubricating oil additives. In general, they are polymers of higher alkyl esters of c p-unsaturated monocarboxylic acids of from 3 t0 8 carbon atoms which contain oil-solubilizing alkyl groups of at least 8 carbon atoms. Illustrative esters of these types include dodecyl methacrylate, octadecyl methacrylate, tridecylacrylate and tetradecyl crotonate. The methacrylates are presently preferred since they provide very satisfactory improvement in the viscosity indexes of lubricating oil compositions. Other monomers, including lower alkyl methacrylates such as butyl methacrylate, may also be copolymerized with the aforementioned higher alkyl methacrylates. Polar monomers such as those characteristic of polymeric detergent additives for lubricating oils may also be included. These polymeric additives are also eifective viscosity index improvers as well as superior detergents. The more suitable polar monomers are the N,N-dialkylaminoalkyl methacrylates such as N,N-diethylaminoethyl methacrylate, the vinyl nitrogen heterocyclic compounds such as vinyl pyridine and vinyl pyrolidone and the polyglycol monomethacrylates such as the dodecyl ether of octadecaethyleneglycol monomethacrylate. V v

Polymeric methacrylate. viscosity index improvers of the above-mentionedtypes are generally characterized'by molecular weightsin the range of 100,000to 300,000 and higher. In the case of'the detergent polymeric compounds, the polar monomers are ordinarily present in proportions of from about 0.1 to about 35.0 percent by weight of the polymer.

The mineral lubricatingoil of the lubricant composi- 4 to present the greatest viscosity stability problem and, therefore, have particular application to the compositions of the invention.

Further illustrations of the improved mineral lubricating oil compositions according to the present invention are provided by the following examples. Unless otherwise specified the proportions in the examples are on a weight basis.

Several mineral lubricating oil compositions containing the typical polymethacrylate thickeners referred to above and the metal salt organic detergent additives were prepared to show the effect of the metal salt additives on the thickened mineral lubricating oil compositions. In the compositions the base oil was a Mid-Continent paraffinic 200 neutral solvent refined mineral lubricating oil having a. viscosity of 200 SSU at 100 F. The oil was thickened with 6 percent by weight of the copolymer of a mixture of dodecyl methacrylate, octadecyl methacrylate, butylvacrylate and N-vinylpyrrolidone in which there are approximately parts by weight of the dodecyl and octadecyl methacrylates, approximately 25 parts by weight of butylacrylate and approximately 10 parts by weight of N-vinylpyrrolidone. The copolymer has an average molecular weight of approximately 150,000 to 200,000. Various metal salt detergent additives are added to the thickened mineral lubricating oil and the effect on the viscosity of the oil in Saybolt Seconds Universal (SSU) at 210 F. is observed as indicated in the following table. The proportions of the metallic salt detergent additives are given in millimoles per kilogram (mM./kg.).

1 Tetradecyl phenatc derived from a mixture of propylene tctramer alkylated phenols having an average of approximately 14 carbon atoms in the alkyl group.

According to the above test results, it will be seen that the important metallic salt detergent additives of the alkaline earth metal petroleum sulfonate, alkaline earth metal phenate and zinc aromatic dithiophosphate types all have an adverse effect on the viscosity of the thickened mineral lubricating oil. The unusual nature of the viscosity stability problem shown by the above test data is emphasized by the fact that certain other metal salt detergent additives such as the zins dialkyl dithiophosphates do not have any such adverse effect on the viscosity of the thickened mineral lubricating oil.

The effect of the inclusion of a dialkyl acylamide containing from 1 to 3 carbon atoms in each alkyl and acyl group in the thickened mineral lubricating oil compositions containing metal salt detergent additives in accordance with this invention is shown by a numberof examples. Test results illustrating the viscosity-temperature characteristics of these examples are given in the following table.

Oil A in the table is the thickened oil described above consisting of a 200 neutral solvent-refined mineral lubricating oil containing 6% by weight of methacrylate and vinylpyrrolidone copolymer.

Oil B is the thickened oil plus 25 mM./kg. of calcium petroleum sulfonate (base ratio 0.4) having an average molecular weight of approximately 500, and 35 mM./kg. of sulfurized calcium tetradecyl phenate (as previously described).

Oil C is a thickened oil consisting of a 150 neutral solvent-refined mineral lubricating oil containing 7.1% by weight of the copolymeric thickener described above.

Oil D is the immediately preceding thickened oil containing 28 mM./kg. of calcium petroleum sulfonate be present in amounts in the range of from 0.05 to 1.0%..

by weight of the composition. Iclaim: I V 1. A lubricating oil composition comprising a major.

portion of a mineral lubricating oil, from 0.1 to 10.0%

0) (base ratio 0.4) having an average molecular weight of by weight of oil-soluble copolymer of (A) ester selected approximately 500, 6.5 mM./kg. sulfurized calcium tetrafrom the group consisting of alkylacrylates and alkyl decyl phenate and mM./kg. zinc butyl hexyldithiomethacrylates having alkyl groups containing from .4 phosphate. to 6 carbon atoms each, (B) ester selected from the Table [I Viscosity Viscosity Viscosity Viscosity Percent Oil at 0 F., at 210 F., Increase, Correction, Improve SSU ssU 210 F., 210 F., ment SSU v SSU A-(Thicknened Oil 7. 800 63.0 B(Thickened Oil+Metal Salt) 33,000 r 79.5 10.5 B-(Thickened 0il+Metal Salt)+ dimethyl acetamide 14, 100 69.4 10.1 61 B-(Thickened Oil+Metal Salt)+ dimethyl formamide 14, 100 69. 7 9. 8 60 C-(Thickened on) 2,800 57.2 D-(Thickened Oil-l-Metal Salt) 8, 100 64. 4 7. 2 D-(Thickened 0i1+Metal Salt)+0.1% dimethyl acetamide 6, 300 61. 4 3. 0 42 D(Thickened Oil+Metsl Salt)+O.1% dimethyl iormamide 6, 600 62. 2 2. 2 31 In the above-described test results addition of alkyl acylamide to the lubricating oil compositions is shown to overcome substantially all the adverse effect on the viscosity incurred by the addition of the metal salt to the thickened oil. The alkyl acylamides as a group are surprisingly better than other polar compounds in their improving ability while the dimethyl acetamide is the best.

Experiments were also carried out with the mineral lubricating oil compositions of the invention to illustrate the stability of their desirable viscosity-temperature characteristics over extended periods of time such as those encountered under normal storage conditions. A number of samples of thickened oils and metal salts, as described in connection with oil D above, were treated with varying amounts of dimethyl formamide and dimethyl acetamide. The results of these tests are given in Table III as follows:

Table III Additive 0 Days Days Days None 142 137 i 137 0.1% Dimethyl Acetamide 148 148 148 0.1% Dimethyl Formamide 146 145 146 'the viscosity indexes of such compositions are stable throughout the extended period of 30 days storage time.

In the foregoing description of the mineral'lubricating oil compositions of the invention, the essential portions of the polymetric thickening additive, the metal salt and the alkyl acylamide have been described asconsisting of alkylacrylates and alkylmethacrylates hav ing alkyllgroups'in the range of 12 to 20carbonatoms each and (C) vinylpyrrolidone, said copolymer ha'vin group consisting of alkylacrylates and alkylmethacrylates having alkyl groups containing from 12 to 20 carbon atoms each and (C) vinylpyrrolidone, said copolymer having a molecular weight in the range of 100,000 to 300,000 and said vinylpyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from 5 to millimoles per kilogram of a metal salt organic a detergent additive selected from the class consisting of neutral alkaline earth'metal petroleum sulfonate, alka- 1 line earth metal phenate, sulfurized alkaline earth metal phenate and zinc aromatic dithiophosphate in which the aromatic groups are selected from the ciassconsisting of alkylphenyl and alkylnaphthyl groups and from, 0.05 to 1.0% by weight of dialkyl acylamide containing from 1 to 3 carbon atoms in each of the alkyl groups and the acyl group. g 2. A lubricating oil composition comprising a major i portion of a mineral lubricating oil, from,0.1 to 10.0% by weight of oil-soluble copolymer of (A) ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the rangeof H 4 to 6 carbon atoms each, (B) ester selected from the; group consisting of alkylacrylates and alkylmethacrylates. having alkyl groups in the range of 12 to 20"carbon' H atoms each and (C) vinylpyrrolidone, said. copolymer 7, having a molecular weight in the range of 100,000 ,to/ 300,000 and said vinylpyrrolidone being from about 0.1,; to about 35.0% by weight of the copolymer, from 510; 100 millimoles per kilogram each of neutral calcium petroleum sulfonate, sulfurized calcium tetradec'yl." phenate and zinc butyl hexyl dithiophosphate and from 0.05 to 1.0% by weight of dimethyl acetamide. I 3. A lubricating oil composition comprising almajor portion of a mineral lubricating oil, from 0.1 to 10.0.? by weight of oil-soluble copolymer of (A) ester selected from the group consisting of alkylacrylates and alkyl methacrylates having alkyl groupsin the range of 4 t s 6 carbon atoms each, (B) ester selected from the group I a-molecular weight in the range of 100,000fto 300,000; and said vinylpyrrolidone being from about 10.1 toabou 35.0% by weight of the copolymer, from} to 100 moles per kilogram each of neutral calcium'petro sulfonate, sulfurized. calcium tetradecyl 'phetiat from 0.05 to 1.0% by weight ofdirnethyl .aceta nu c 4. A lubricating oil composition comprising a portion of a mineral lubricating oil, from 0.1 to 10.0% by weight of oil-soluble copolymer of (A) ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 4 to 6 carbon atoms each, (B) ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 12 to 20 carbon atoms each and (C) vinylpyrrolidone, said copolymer having a molecular weight in the range of 100,000 to 300,000 and said vinylpyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from 5 to 100 millimoles per kilogram each of neutral calcium petroleum sulfonate, sulfurized calcium tetradecyl phenate and zinc butyl hexyl dithiophosphate and from 0.05 to 1.0% by weight of dimethyl formamide.

5. A lubricating oil composition comprising a major portion of a mineral lubricating oil, from 0.1 to 10.0% by weight of oil-soluble copolymer of (A) ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 4 to 6 carbon atoms each, (B) ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 12 to 20 carbon atoms each and (C) vinylpyirolidone, said copolymer having a molecular weight in the range of 100,000 to 300,000 and said vinylpyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from 5 to 100 millimoles per kilogram each of neutral calcium petroleum sulfonate and sulfurized calcium tetradecyl phenate and from 0.05 to 1.0% by weight of dimethyl formamide.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,048 Michaels et a1. July 1, 1952 2,715,107 Talley et a1. Aug. 9, 1955 2,833,719 Van Horne et a1. May 6, 1958 FOREIGN PATENTS 735,711 Great Britain Aug. 24,1955 

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PORTION OF A MINERAL LUBRICATING OIL, FROM 0.1 TO 10.0% BY WEIGHT OF OIL-SOLUBLE COPOLYMER OF (A) ESTER SELECTED FROM THE GROUP CONSISTING OF ALKYLACRYLATES AND ALKYLMETHACRYLATES HAVING ALKYL GROUPS CONTAINING FROM 4 TO 6 CARBON ATOMS EACH, (B) ESTER SELECTED FROM THE GROUP CONSISTING OF ALKYLACRYLATES AND ALKYLMETHACRYLATES HAVING ALKYL GROUPS CONTAINING FROM 12 TO 20 CARBON ATOMS EACH AND (C) VINYLPYRROLIDONE, SAID COPOLYMER HAVING A MOLECULAR WEIGHT IN THE RANGE OF 100,000 TO 300,000 AND SAID VINYLPYRROLIDONE BEING FROM ABOUT 0.1 TO ABOUT 35.0% BY WEIGHT OF THE COPOLYMER, FROM 5 TO 100 MILLIMOLES PER KILOGRAM OF A METAL SALT ORGANIC DETERGENT ADDITIVE SELECTED FROM THE CLASS CONSISTING OF NEUTRAL ALKALINE EARTH METAL PETROLEUM SULFONATE, ALKALINE EARTH METAL PHENATE, SULFURIZED ALKALINE EARTH METAL PHENATE AND ZINC AROMATIC DITHIOPHOSPHATE IN WHICH THE AROMATIC GROUPS ARE SELECTED FROM THE CLASS CONSISTING OF ALKYLPHENYL AND ALKYLNAPHTHYL GROUPS AND FROM 0.05 TO 1.0% BY WEIGHT OF DIALKYL ACYLAMIDE CONTAINING FROM 1 TO 3 CARBON ATOMS IN EACH OF THE ALKYL GROUPS AND THE ACYL GROUP. 